Can you refocus your eye to cheat on an eye exam?

My son was recently prescribed hos first pair of glasses, and they are kind of strong for his first pair (-2 in each eye). When his eyes were checked, asked him to read a chart from 20 feet away and put different power lenses in a viewer and had him read charts through the viewer to see which power he could see clearly through, and he was able to read everything accurately with the prescription he currently has. My wife wears glasses, and I can see perfectly with her glasses on if I purposely blur my vision. My son and wife are not related, so theres no way he got his bad vision from her, and he did not want to dialate his pupils either, so I feel like he purposely blurred his vision to fail, is that possible?

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